Reanalysis Comparison Update 2023

This post provides a brief comparison update of two different reanalysis daily global mean surface air temperature anomaly (GMSATA) time series for 2014 through 2023 January 31. The graph in Figure 1 shows the daily GMSATA time series for the Climate Forecast System Reanalysis (CFSR) output based on the Global Forecast System (GFS) initialization output four times each day. The temperature output is for the atmosphere at 10 meters above ground level. The CFSR model uses a 0.5 degree latitude by 0.5 degree longitude grid.

Figure 1. CFSR GMSATA 2014-2024 (click on image to enlarge)

The graph in Figure 2 shows the daily GMSATA time series for the Sigma 0.995 level output from the National Centers for Environmental Prediction and National Center for Atmospheric Research Reanalysis 1 (NCAR R1) cooperative effort. The Sigma 0.995 level corresponds to the pressure altitude at 99.5 % of the surface air pressure, which is roughly about 50 meters above ground level. The actual height above ground level varies somewhat depending on atmospheric conditions. The NCAR R1 model uses a 2.5 degree latitude by 2.5 degree longitude grid.

Figure 2. NCAR R1 GMSATA 2014-2024 (click on image to enlarge)

Figure 3 provides the NCAR R1 daily GMSATA time series for the current century beginning in 2001.

Figure 3. NCAR R1 GMSATA 2001-2024 (click on image to enlarge)

For a broader perspective, Figure 4 provides the NCAR R1 daily GMSATA time series for its entire period of record, beginning in 1948.

Figure 4. NCAR R1 GMSATA 1948-2024 (click on image to enlarge)

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Comparison of NCEP CFSR versus NCDC Global Temperature Anomalies

The US National Center for Environmental Prediction (NCEP) has produced a Climate Forecast System Reanalysis (CFSR) based on “all available conventional and satellite observations”.  Most of these data were used to initialize real-time global weather forecast model runs four times each day since 1979.  This reanalysis can also be used to estimate annual global temperatures and temperature anomalies.  The University of Maine Climate Change Institute has compiled the CFSR data and provided an easy-to-use interface for viewing some of the data using maps and graphs with their Climate Reanalyzer web site.

I pulled CFSR annual global temperature anomaly data from the Climate Reanalyzer for 1979 through 2013 and added a compatible estimate for 2014 from the Weather Bell model temperature web page to complete the period 1979-2014.  I then graphed this data against the US National Climatic Data Center (NCDC) estimates based on the Global Historical Climate Network (GHCN) for the same period, as shown in Figure 1 below.  Both data sets have been normalized to the 1981-2010 period for comparison.

Figure 1. Comparison of NCEP CFSR versus NCDC estimates of annual global temperature anomalies from 1979 through 2014.

In general, the two approaches show a similar result, but there are some interesting differences.  These differences help to indicate some of the uncertainty in trying to estimate a global temperature anomaly as discussed in my previous post.  Of particular interest is the result for the most recent portion from 2001 through 2014.  The “pause” in the NCDC estimates is actually more of a peak and decline in the CFSR estimates.  The warmest years in the CFSR estimates are 2002-2003 and 2005-2007 with a peak in 2005.  In contrast, the warmest year estimated by NCDC is 2014.  In the CFSR data, 2014 ranks 12th for the 36-year period – far from being the “hottest year ever” as promoted by some.

Considering that the NCEP CFSR approach incorporates a much larger data set with much better spatial coverage for estimating global temperatures than the NCDC GHCN approach, I suspect the CFSR annual estimates are more accurate.

Interglacial Comparisons

Most people don’t realize that the Earth is still in a long term ice age that started about three million years ago and has had many alternating cold glacial periods interspersed with warmer interglacial periods.  We are currently in an interglacial period where global temperatures have been near our modern “normal” for about 12,000 years now.  In addition to our current interglacial period, there have been four previous interglacial periods in the last 500,000 years.  Each one has been spaced about 100,000 years apart and lasted about 2,000 to 25,000 years with temperatures at or above our current modern “normal”.  These observations are based on the EPICA Antarctic ice core climate reconstruction using oxygen isotope ratios as a proxie for global temperature change.

The graph below shows the current and last four interglacial periods plotted together, normalized to the year where the estimated global temperature first reached the level of our modern “normal” climate. The approximate year where each interglacial episode first reached the modern “normal” temperature is shown in the legend.  Notice that all four previous interglacials had global temperatures reaching 2 to 4 degrees Centigrade higher than our current modern “normal” without any help from humans, based on this reconstruction.

This graph compares the current interglacial period with the previous four interglacials using the EPICA ice core climate reconstruction. Each interglacial period has been normalized to the time the global temperature departure first reached the current “normal” temperature. Click on graph to enlarge.

I find it amazing how abruptly and similarly each glacial period ended in about 5,000 years to start each following interglacial warm period.  In contrast, the duration of the interglacials has been much more variable. The most recent previous interglacial period that started about 130,000 years ago lasted about 14,000 years at temperatures at or above our current modern “normal”. The second previous interglacial lasted about as long as our current interglacial while the third previous was by far the shortest, lasting about 2,000 years, but arguably had somewhat of a double peak. However, the latter secondary peak did not quite reach the warmth of our current modern “normal”. The fourth previous interglacial which started about 418,000 years ago was by far the longest at about 25,000 years.

As repeatable as the glacial cycles have been over the last 500,000 years, I see little reason not to expect more of the same in the future. Using this interglacial comparison as a climate persistence forecast, we might expect about a 75% chance that the global average temperature will begin to drop dramatically sometime within the next few thousand years and about a 25% chance of staying warm for another 10,000 years or so … at most. Perhaps we need all the anthropogenic warming we can muster to stall or prevent the next glacial period?

Our understanding of what causes these glacial cycles, which are relatively recent on a geological scale, is still very limited although there are plenty of hypotheses. Our current climate models cannot predict them and therefore to me are somewhat useless. Until we can create climate models that can accurately track past glacial and interglacial periods I will not be too impressed and I certainly don’t believe our infant and untested climate models should be used to shape policy regarding “climate change”.

Update 2016 November

Below is a link to an interesting analysis of the causes of glacial cycles, along with conclusions made by the author, which seem reasonable to me.  The author hypothesizes that evidence suggests that the current interglacial period is likely to be only average in length and therefore should be ending soon, most likely sometime within the next two thousand years.

Nature Unbound I: The Glacial Cycle

Conclusions

1) Obliquity is the main factor driving the glacial-interglacial cycle. Precession, eccentricity and 65°N summer insolation play a secondary role. There is no 100 kyr cycle. Milankovitch Theory is incorrect.

2) The current pacing of interglacial periods is the consequence of the Earth being in a very cold state that prevents almost half of obliquity cycles from successfully emerging from glacial conditions. The rate for the past million years has been 72.7 kyr/interglacial, or 1.8 obliquity cycles between interglacials. This can be generally described as one interglacial every two obliquity cycles except when close to the 413 kyr eccentricity peaks, when interglacials take place at every obliquity cycle.

3) Glacial terminations require, in addition to rising obliquity, the existence of very strong feedback factors manifested as very low glacial maximum temperatures. High northern summer insolation at the second half of the rising obliquity period is a positive factor, and if high enough during eccentricity peaks can drive the termination process.

4) CO2 can only produce a minor effect in glacial terminations since the measured change in concentration (roughly a third of a doubling which represents half of the warming effect of a doubling) is too small to account for any important contribution to the large observed temperature changes.

5) Since the precession cycle has bottomed and the obliquity cycle is half way down we should expect the next glacial inception to take place within the next two millennia.